The nation’s most prolific serial killer marked his 62nd birthday Friday by pleading guilty to his 49th murder.

Gary L. Ridgway, who spent years prowling for teenage girls and women on the fringes of society, admitted to a packed Kent courtroom that among his first victims was a 20-year-old prostitute named Rebecca “Becky” Marrero.

Marrero was last seen walking out of a SeaTac motel on Dec. 3, 1982, leaving behind her 3-year-old daughter, her boyfriend and her sister.

Speaking on behalf of the family, Mary Marrero, the victim’s sister, called Ridgway “a waste to society and a waste of space.”

“I hate your guts, Gary Ridgway, and your day is coming soon,” she said as her mother and another relative stood close by.

Ridgway admitted to killing Marrero years ago, but her remains weren’t found until December. The discovery, in an Auburn ravine, allowed King County prosecutors to charge the so-called Green River Killer with aggravated murder in her slaying.

With Marrero’s family seated nearby in the courtroom at the Maleng Regional Justice Center, Ridgway was sentenced to an additional count of life in prison. Because of his previous confession to killing Marrero, the new murder charge falls under the terms of the 2003 plea agreement that spared him from a potential death penalty, King County prosecutors said.

After Ridgway’s arrest in 2001, then-King County Prosecutor Norm Maleng agreed he would not seek the death penalty against him in exchange for his cooperation in locating the remains of dozens of victims. Ultimately, Ridgway admitted to nearly 70 slayings, but at the time prosecutors said they only had evidence linking him to 48 cases.

Ridgway appeared in court dressed in an orange Department of Corrections (DOC) jumpsuit. He was surrounded by eight officers from the King County Jail, state DOC and court security.

After entering his guilty plea, Ridgway answered “yes” to a series of questions from King County Senior Deputy Prosecutor Jeff Baird, who sought to make sure he understood the ramifications of his plea. Ridgway showed little emotion.

Superior Court Judge Mary Roberts, at the conclusion of the nearly 30-minute hearing, told Ridgway that she had very little to say to him. She said she often tries to offer defendants “some humanity,” but in his case she said she could “find no compassion.”

Mary Marrero described the toll her sister’s death has taken on her family.

“It’s been a long 29 years without Becky Marrero,” she said.

She said she didn’t agree with the plea deal that spared Ridgway from the death penalty.

“What does it take to get the death penalty in the state of Washington, your honor?” she said to the judge. “It makes me sick to my stomach that he beat the system.”

Ridgway was given a chance to speak during Friday’s hearing but managed only a few words — “I’m sorry for putting the family through this … ” — before he was shouted down by a man identified by family members as Becky Marrero’s brother. The man, who did not give his name, shouted curses at Ridgway and told him to sit down.

In December, three teens stumbled upon Marrero’s remains in a ravine in the 6300 block of 296th Street, just west of West Valley Highway North. The area is near where Ridgway disposed of another victim.

Earlier this month, after charging Ridgway with the new slaying, King County Prosecutor Dan Satterberg said the sentencing would give Marrero’s family a chance to face her killer.

“They finally have answers, and with the anticipated guilty plea they will obtain the truth,” Satterberg said at the time.

After Ridgway was charged with Marrero’s slaying, defense attorney Mark Prothero said Ridgway wanted “to step up and take responsibility for it now.”

Marrero fit the profile of Ridgway’s victims, mostly young runaways, prostitutes or drug addicts picked up on Pacific Highway South.

Ridgway provided authorities with several locations where he thought Marrero’s body could be found, from Tukwila to Interstate 90, according to court documents. With dozens of victims, the Green River killer couldn’t remember exactly where he disposed of the body, “but said he was sure it would eventually be found,” the documents said.

Among the observers in court Friday was Virginia Graham, of Spokane, the sister of Ridgway victim Debra Lorraine Estes, 15. She said Estes and Marrero were childhood friends.